Numbering the elements of a list

Question

From a vector q={Gamma,x,y}, I would like to create the following corresponding list : qn={1,2,3}.

Other example, if I have q={Gamma,x,y,theta}, I would like to retrieve qn={1,2,3,4}.

Thank you for your help.

Is there a better way than Table[i, {i, 1, Length[q]}]?

Thank you

$\begingroup$ Range[Length[q]] $\endgroup$ – Jason B. Nov 12 '15 at 10:26 — Jason B., Nov 12 '15 at 10:26
$\begingroup$ @JasonB probably you should post it as an answer. $\endgroup$ – rhermans Nov 12 '15 at 10:38 — rhermans, Nov 12 '15 at 10:38
$\begingroup$ Right! For me, it is perfect. Thank you $\endgroup$ – Bendesarts Nov 12 '15 at 10:39 — Bendesarts, Nov 12 '15 at 10:39
$\begingroup$ What would you like to get for {Gamma, x, x, Gamma}? $\endgroup$ – Kuba♦ Nov 12 '15 at 10:44 — Kuba♦, Nov 12 '15 at 10:44

Jason B. · Accepted Answer · 2015-11-12 10:40:52Z

4

This will give what you are looking for

q = {Gamma, x, y, theta};
Range[Length[q]]
(* {1, 2, 3, 4} *)

Or, with less typing,

Range@Length@q
(* {1, 2, 3, 4} *)

answered Nov 12 '15 at 10:40

Jason B.

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eldo · Accepted Answer · 2015-11-12 10:42:35Z

2

As @Jason already commented, the usual form would be

Range @ Length @ q;

If your goal is to number the list you can do

> Transpose[{Range @ Length @ q, q}]

{{1, Gamma}, {2, x}, {3, y}, {4, theta}}

or use MapIndexed

MapIndexed[List, q]

{{Gamma, {1}}, {x, {2}}, {y, {3}}, {theta, {4}}}

answered Nov 12 '15 at 10:42

eldo

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$\begingroup$ Or, do MapIndexed[Reverse@*Flatten@*List, q] to get it in the normal form. $\endgroup$ – march Nov 12 '15 at 17:17

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2 Answers 2